1. Field of Invention
Embodiments of the invention generally relate to systems and methods of processing hydrocarbons. More specifically, embodiments of the invention relate to recovery of natural gas liquids and a pressurized methane-rich sales gas from liquefied natural gas.
2. Description of Related Art
Natural gas is commonly recovered in remote areas where natural gas production exceeds demand within a range where pipeline transportation of the natural gas is feasible. Thus, converting the vapor natural gas stream into a liquefied natural gas (LNG) stream makes it economical to transport the natural gas in special LNG tankers to appropriate LNG handling and storage terminals where there is increased market demand. The LNG can then be revaporized and used as a gaseous fuel for transmission through natural gas pipelines to consumers.
The LNG consists primarily of saturated hydrocarbon components such as methane, ethane, propane, butane, etc. Additionally, the LNG may contain trace quantities of nitrogen, carbon dioxide, and hydrogen sulfide. Separation of the LNG provides a pipeline quality gaseous fraction of primarily methane that conforms to pipeline specifications and a less volatile liquid hydrocarbon fraction known as natural gas liquids (NGL). The NGL include ethane, propane, butane, and minor amounts of other heavy hydrocarbons. Depending on market conditions it may be desirable to recover the NGL because its components may have a higher value as liquid products, where they are used as petrochemical feedstocks, compared to their value as fuel gas.
Various techniques currently exist for separating the methane from the NGL during processing of the LNG. Information relating to the recovery of natural gas liquids and/or LNG revaporization can be found in: Yang, C. C. et al., “Cost effective design reduces C2 and C3 at LNG receiving terminals,” Oil and Gas Journal, May 26, 2003, pp. 50-53; US 2005/0155381 A1; US 2003/158458 A1; GB 1 150 798; FR 2 804 751 A; US 2002/029585; GB 1 008 394 A; U.S. Pat. No. 3,446,029; and S. Huang, et al., “Select the Optimum Extraction Method for LNG Regasification,” Hydrocarbon Processing, vol. 83, July 2004, pp. 57-62.
There exists, however, a need for systems and methods of processing LNG that increase efficiency when separating NGL from a methane-rich gas stream. There exists a further need for systems and methods of processing LNG that enable selective diverting of the LNG to a flow path that vaporizes both methane and ethane plus within the LNG.